(a) Technical Field
The present invention relates to a fuel cell stack that prevents deterioration of an end cell. More particularly, the present invention relates to a fuel cell stack that prevents deterioration of an end cell, which has a structure for preventing cooling of a neighbor cell adjacent to a closed end plate.
(b) Background Art
A fuel cell stack is a kind of generating device that generates electricity as a major energy source of a fuel cell vehicle and has a structure in which an anode to which hydrogen is supplied and a cathode to which oxygen is supplied are stacked with a membrane electrode assembly interposed therebetween such that oxygen-containing air and externally supplied hydrogen chemically react with each other to generate electrical energy.
In general, a fuel cell stack is configured in such a manner that several tens to several hundreds of unit cells are stacked. The configuration of a unit cell of the fuel cell stack will be described below. More specifically, a membrane electrode assembly (MEA) is positioned in the center of a unit cell. The membrane electrode assembly includes a polymer electrolyte membrane capable of transporting hydrogen ions (protons) and a cathode electrode (catalyst) and an anode electrode (catalyst), which are stacked on both sides of the electrolyte membrane such that hydrogen and oxygen react with each other. Moreover, a gas diffusion layer (GDL) is stacked on the outside of each of the cathode electrode and the anode electrode, and a separator in which flow fields are formed to supply fuel and discharge water produced by a reaction is stacked on the outside of the gas diffusion layer.
Furthermore, after several tens to several hundreds of unit cells are stacked, an end plate for supporting and fixing the respective components is connected to both outermost sides as schematically shown in FIG. 1, thus completing the fuel cell stack. Here, the end plate serves as a support for fastening of the fuel cell stack and a transfer path of generated electricity. The end plate is typically made of plastic and metal.
As shown in FIG. 1, when several hundreds of unit cells of a fuel cell stack 10 are stacked, a dummy cell 14 is stacked in a position adjacent to a closed end plate 22 other than working cells 12 in which an electricity generation reaction takes places. Also, a supply manifold 16 is formed on one side vertically in the stacked direction of the working cells 12 and the dummy cell 14, and a discharge manifold 18 is formed on the other side vertically.
In particular, as shown in FIG. 1, the end plate on one side is configured as a closed end plate 22 with a closed structure, and the end plate on the other side is configured as an open end plate in which an inlet path 26 for introducing hydrogen, air, and coolant is formed in an upper end and an outlet path 28 for discharge of unreacted gas and coolant is formed in a lower end.
In general, the fuel (hydrogen and air) and coolant supplied to the fuel cell stack sequentially pass through the open end plate 24, the supply manifold 16, the working cells 12, the discharge manifold 18, and the open end plate 24 again and is then discharged to the outside of the fuel cell stack. In detail, the hydrogen is supplied to the anode through the inlet path 26 of the open end plate 24, the air (oxygen) is supplied to the cathode, and the coolant for cooling is supplied to a coolant flow field of the separator also through the inlet path 26 of the open end plate 24.
Accordingly, at the anode of the fuel cell stack, an oxidation reaction of hydrogen occurs to produce hydrogen ions (protons) and electrons, and the produced hydrogen ions and electrons are transmitted to the cathode through the polymer electrolyte membrane and the separator. At the cathode, the hydrogen ions and electrons transmitted from the anode react with the oxygen-containing air to produce water. At the same time, electrical energy is generated by the flow of electrons.
Meanwhile, the fuel (hydrogen and air) supplied to the fuel cell stack should be humidified to maintain the performance of the membrane, and thus when the humidified fuel supplied to the fuel cell stack passes through the supply manifold, condensed water is produced due to a low ambient temperature. Here, the produced condensed water is introduced into the fuel cell stack along the wall of the flow field together with the fuel, and the performance and durability of the cells into which the condensed water is introduced are degraded as a result, which may be caused by catalyst deterioration due to the continued presence of water around the catalyst.
Moreover, the cells adjacent to the end plates 22 and 24 have a temperature lower than that of other cells due to cooling from external environments through the end plates 22 and 24. In particular, the cell adjacent to the closed end plate 22 is further cooled, when the fuel and coolant hit the inside wall of the closed end plate 22, and thus has a much lower temperature. The low temperature of the cells increases the production of condensed water in the cells, which causes the deterioration of the fuel cell stack.
Conventionally, to solve this problem, as shown in FIG. 1, the dummy cell 14 (i.e., a non-reaction cell that does not generate electricity but serves as a discharge path of condensed water) is provided in a position adjacent to the closed end plate 22, but its effect is insignificant. As a result, the deterioration of durability performance continuously occurs in the cell adjacent to the closed end plate 22. Accordingly, a dummy cell may be further provided in a position adjacent to the closed end plate 22 to prevent the deterioration of durability performance due to cell cooling but, in this case, various problems such as a reduction in output, an increase in manufacturing cost, an increase in weight, etc. occur due to the additional application of the dummy cell.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.